Method of producing a photographic



United States Patent METHOD OF PRODUCING A PHOTOGRAPHIC IlVIAGE BY PHYSICAL DEVELOPMENT Cornelis Johannes Dippel and Harke Jan HoutmamEindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn, as trustee No Drawing. Application March 18, 1952, Serial No. 277,276

Claims priority, application Netherlands March 27, 1951 11 Claims. (Cl. 95-88) This invention relates to a method for obtaining photographic contrasts with the aid of light.

It is known to obtain photographic contrasts by exposing a carrier which has been sensitised with a diazosulphonate followed by reacting the light-decomposition product produced upon exposure with a mercurous salt to form a latent mercury image which can be intensified by physical development, this term being understood to mean a method of developing according to which, prior to development, not all the metal required for building up the contrast, is present as silverions out of crystallised compounds already present on the same spot that is blackened afterwards by this development. During this process a phenomenon, hereinafter referred to as regression occurs in which the sensitivity of the exposed carrier decreases as the length of time between exposure and formation of the latent mercury image increases. 7

It is an object of the present invention to increase and to stabilise the sensitivity of light-sensitive systems containing a diazosulphonate which are reacted with a mercurous salt, the latent mercury image thus produced being subjected to physical development.

In accordance with the invention, the decrease in sensitivity of the light-exposed diazosulphonate is substan tially prevented by incorporating into the light-sensitive anti-regression agent which suppresses the tendency of the sensitivity of the exposed diazosulphonate to decrease. The term anti-regression agent as used throughout the specification and in the claims is defined as a substance which prevents the light-decomposition product formed upon exposure to light of the diazosulphonate from reverting to the diazosulphonatc and thereby suppresses the tendency of the sensitivity of the exposed light-sensitive diazosulphonate to decrease. Among the anti-regression agents suitable for the invention are one or more of the following: i

(a) Water-soluble salts having ions which greatly reduce the concentration of sulphite ions in water and which do not oxidize mercurous salts nor react therewith with separation of mercury and/or insoluble mercury compounds and whose sulphite compounds are capable of reacting with mercurous ions with separation of metallic mercury.

(b) Cations falling under a in the form of salts of the photosensitive diazosulphonic acid having these ions.

(c) Water-soluble weak acids and salts thereof having an acid reaction in solution and mixtures, having an acid reaction, of salts thereof with acids and which otherwise satisfy the conditions mentioned under a.

(d) Fast-coupling azocomponents which neither oxidize mercurous salts nor react therewith with separation of mercury and/or insoluble mercury compounds.

(e) Soluble aromatic monoand polysulphonic acids and soluble salts thereof which do not oxidize mercurous salts and do not react therewith with separation of mercury and/or. insoluble mercury compounds.

(f) Salts of the cations falling under a with the acids mentioned under e.

" A 2,735,773 Ice A Patented Feb. 21, 1956 (h) Mixtures of substances mentioned under a to g in so far as they do give no undesired reactions with one another.

Examples of suitable salts, as mentioned under a, are:

-lead acetate-lanthanum (III) nitrate-thorium (IV) nitrate-uranyl acetate-cadmium lactate-zinc acetate-chromium (III) acetate-copper (II) acetate-cobalt acetate.

Examples of salts according to b are: paramethoxybenzene diazosulphonic acid lead salt; methyl-1 chloro-3 benzene-diazosulphonic acid-4 zinc salt.

Examples of suitable acids according to c are: lactic acid and citric acid. Use may be made of mixtures of their alkali salts with the free acid but preferably the salts of the cations falling under a or mixtures thereof are used.

As a rule, in view of the durability of the photosensitive layer non-volatile acids and salts of such acids should be used.

Examples of fast-coupling azo-components according to d are resorcinol; ,B-naphthol; amino-l naphthol8 bisulphonic acid-3.6.

Examples of aromatic monoor polysulphonic acids according to e are: naphthalene trisulphonic acid and metasulphobenzoic acid.

Examples falling under are: naphthalene-bisulphonic acid lead and a-naphthylarnine sulphonic acid cadmium.

Example falling'under g is: ammonium tungstenate.

In all these cases mentioned under a to h, for the purpose of avoiding fog, the pH-value of the solution with which the layer is treated prior to exposure must be less than 7 and accordingly the solution, if necessary, must therefore be admixed with free acid.

While the following explanation is advanced to explain the phenomenon of regression, it is to be understood that it forms no part of the invention. Regression is believed to be due to the nature of the variation to which the'diazosulphonate is subjected under the action of the incident light. The resultant light reaction product results in sulphite ions being available which are capable of releasing metallic mercury from mercurous salts. This metallic mercury forms the metal image which can be intensified by physical development. The above cited substances can act as antiregression agents if it is assumed that light reaction converts tthe diazosulphonic acid into an isomeric sulphite compound from which sulphite ions are readily split off and also assuming the reaction to be reversible so that at the end of the exposure the diazosulphonic acid is again formed.

The antiregression agents are substances which obstruct or prevent the occurence of this reverse re tion. This prevention or obstruction may be effectthcr by combination of the molecule part which con the diazonium group, the sulphite being thus'set free or not being capable of combining again to form diazosulphonic acid, or by combining with the sulphite. it may be as sumed that in the dry layer to which the antiregression agent has been added, the number of the free diazonium ions and free sulphite ions is thus reduced to an extent such that the velocity of their reaction has become substantially nil. Accordingly, there is no objection to a fixed bond of the diazo part but the bond of the sulphite must be such that the bound sulphite is still capable of reacting to form mercury with the mercurous ions which are subsequently added. Finally, as an alternative, an antiregression agent may be added which reacts both with the diazo part and with sulphite.

Consequently, it may be assumed that for example the fast-coupling ale-components mentioned under a, such for. example as resorcinol, react with the diazonium 3 residue of the exposed diazo sulphonic acid, whereby a dyestuif may be produced and whereby the released sulphite ions are prevented from again forming the diazosulphonic acid in the absence of the diazonium compound. l

The same remark applies to the aromatic sulphonic acids mentioned under e which combine with diazonium residues to form so-called diazoaryl sulphonates.

On the other hand it may be assumed that some antiregression agents react with sulphite and thus prevent the reverse reaction.

Among them are presumably the said acids and salts; in some cases complex-formation may also play a part since in view of the very small quantities of sulphite which are produced by exposure, the low solubility of the compounds produced cannot fully account in many cases for the antiregression effect.

It may be noted that it has been found that tests on solutions in which the quantity of sulphite is determined by analysis are not decisive for the success of the anti regression effect in a support.

A particularly intense antiregression effect was obtained by using, as stated under 1'', as the antiregression agent a suitable salt, for example a lead or cadmium salt, of an aromatic sulphonic acid. The use of lead salts has the advantage that they are generally readily soluble and that both the lead and the sulphonic acid exercise an antiregression effect.

The sulphite ions, which, due to the exposure, are formed from the diazosulphonate abstract mercurous ions from the equilibrium Hgz++ Hg+++Hg This results in the formation of the metallic mercury to form contrasts which can be intensified by physical development to form the metal image. Consequently, in order that satisfactory results may be obtained the reaction of the sulphite ion with the mercurous ion should preferably not be disturbed by any of the substances mentioned under a to h. This accounts for the fact that not all the substances which are capable of combining with the said sulphites are suitable for carrying out the method according to the invention. Thus, for example, the typical sulphite binders, such as the carbonyl compounds (German specification No. 642,223) are not suitable because sulphite combined in this manner no longer reacts with mercurous ions. Likewise oxidizing and reducing substances, which give unwanted reactions with mercurous ions and sulphite ions, and in addition those substances which react excessively slowly with sulphite or diazonium ions respectively are not suitable.

It has been suggested that an azo-component be added to layers containing diazo sulphonate (cf. British specifications 518,129 and 518,162) in order to obtain a dyestulf image after exposure from both substances by coupling, and the use of layers containing diazosulphonate in an azo-component with volatile weak acids or salts thereof, such as zinc salts, is also known from German specification 734,302 and American specification 2,217,189. Formation of a dyestuff image by coupling of the diazosulphonate and the azo-component is prevented in these layers by the said volatile weak acids or their salts, the dyestutf image being then formed after heating by decomposition of the salt or volatilization of the acid respectively and subsequent coupling of the two components under the influence of the residual basic salt or oxide.

In addition layers are known which, for the purpose of deepening the colour of the azo-dyestulf image, have added to them given metal salts, for example copper or chromium salts.

All these admixtures have a function quite different from that of the antiregression agents disclosed hereinabove since they participate in the image formation or assist in or prevent the formation of azo-dyestuffs. However, if with the present invention an azo-component is used this is effected under such conditions that the dyestuff produced is not contained or else does not play an important part in the ultimate image and when using salts of the abovementionedkind .azo-dyestuff is generally, not formed at all but the metal image is produced with far less exposure and with the use of a mercurous compound.

It is preferable that the concentration of the antiregression agent not be less than of that of the diazosulphonate employed. The extent to which the regression is balanced out also depends on the choice of the diazosulphonate and even the material constituting the support for the photo-sensitive system may be of influence on the choice of the concentration. In favourable cases the regression is substantially rejected and cliazosulphonatcs which due to regression were quite unserviceable are rendered substantially useful by the method according to the invention.

Thus, for example, it has been found that except for the use of an antiregression agent the photosensitive compound 2-chlorine 4-methyl benzene diazosulphonic acid sodium-1 exhibits an abnormously low sensitivity, even in the case of very quick operation, and that by addition of, for example, ammonium tungstenate, to the sensitising solution the sensitivity and the blackening obtainable becomes substantially equal to those that can be obtained with paramethoxybenzene-diazosulphonate. It is also found that the colour of the silver image thus becomes deep black.

As the azo-component antiregression agent compounds giving a soluble dyestuff with the exposed diazosulphonate may be conveniently used; for the well-known negativepositive dyestuff-image processes, however, such a combination cannot be used since in this case the whole image disappears during washing. However, this is not a disadvantage in the production of images according to the invention. Moreover, due to the use of much lower quantities of light the dyestutf image is very weak and in so far as it is still present it is fully covered by the developed image.

It has been further found that it is particularly useful to use as the antiregression agent lead salts of aromatic sulphonic acids, Zn-acetate, Cd-lactate.

A suitable test for determining whether or not a substance will be satisfactory antiregression agent is as follows: two solutions of the photosensitive substance are prepared, one with and the other without the substance under examination being provided and soaked therewith are two foils of superficially saponified cellulose-acetate which are exposed in a substantially identical manner behind a sensitometer wedge.

At the end of 10 seconds, 15 minutes and 1 hour respectively the exposed foils are treated in a mercurous salt solution and then physically developed. It will be found that a substance which is effectively active as an antiregression agent the decrease in number or blackening, respectively, of the small steps is less.

The method according to the invention is of prime importance for recording or reproducing various images one after the other on a single piece of material, such, for example, as for microdocumentation. For this purpose, layers eontaining a diazosulphonate may be used.

The method according to the invention is also particularly important for the production of colored images in accordance with Netherlands specification 153,804 because in this case reproducibility is of prime importance, particularly for the production of multi-color images.

Wherever reference is made in this specification to diazosulphonate and diazosulphonic acid they are to be understood to mean one or more organic combinations characterized by the presence of one or more groups N2SO3H or the salts corresponding therewith.

Example I A superficially saponified cellulose-acetate foil was sensitised with a solution containing 0.2 mol. p-methoxybenzene diazosulphonic acid-sodium and 0.003 mol. citric acid per liter of water and dried. The foil was exposed from a 500 watt mercury lamp. The longest exposure 1 time was 45 seconds and the subsequent exposure times each time were smaller than the preceding one by a value V2. Immediately after the exposure the foil was then treated with a solution of 0.02 N mercurous nitrate and physically developed for minutes in a solution which contained 0.5% rnetol', 2% citric acid and 0.2% silvernitrate.

If the sensitivity of the foil without citric acid was taken to be equal to 100, that of the foil containing citric acid equalled 115. If the foil were treated within hour after the exposure of the mercurous nitrate solution, the sensitivity with the foil without citric'acid had fallen to 10 and with that with citric acid to 100 and after 1 hour to 85.

- Example II A foil of the kind used in Example I was sensitised using a solution containing 0.2 mol. p-ethoxy benzene diazosulphonic acid-sodium and 0.1 mol. zinc acetate per liter, of water and then dried. The following exposure, treatment and development were effected as described in Example I. If a foil without zinc acetate were treated with the mercurous nitrate solution immediately after exposure or within A and 1 hour thereafter, the sensitivity was 100 (arbitrarily taken to be 100), 50 and respectively, Whereas those with zinc acetate were 120, 100 and 100 respectively.

Example III A foil as used in Example I was sensitised with a solution containing 0.2 mol. p-methoxy benzene diazosulphonic acid sodium and 0.2 mol. resorcinol per liter of water and then dried. The photo-sensitive foil thus obtained was exposed, treated. and developed as described in Example I. When the foil was stored for 0, A and 1 hour after exposure and then treated with the mercurous salt solution, the sensitivity expressed in terms of the scale of Example I was 60, 35 and respectively.

Example A foil as used in Example I was sensitised with a solution containing 0.2 mol. p-methoxy benzene diazosulphonic acid sodium and 0.1 mol. naphthalene trisulphonic acid per liter of water, then dried and subsequently exposed treated and developed as described in Example I.

The sensitivity (expressed in terms of the scale of Example I) was when the foil was treated with the mercurous nitrate solution immediately, A and 1 hour respectively after the exposure; 115, 80 and 50 respectively.

Example Vl Paper was sensitised with a solution containing 0.2 mol. p-methoxy benzene diazosulphonic acid sodium and 0.1 mol. naphthalene bisulphonic acid-Pb per liter of water then dried and subsequently exposed, treated and developed for 5 minutes as described in Example I. If the sensitivity of paper without naphthalene bisulphonic acid'Pb and treated and developed immediately after exposure is arbitrarily taken to be equal to 100, it was after a time interval of A hour between exposure and treatment: and after 1 hour: 10.

With the foil using this antiregression agent the sensi- 6 tiveness (expressed in the same scale) are 50, 50 and 40 respectively. a

Example VII A foil as used in Example I was sensitised with a solution of 52 g. chloro-Z methyl-4 benzene diazosulphonic acid sodium and 20 g. ammonium tungstenate in ccm. of water.

After drying, exposure, after-treatment and develop ment were performed as described in Example I.

If the sensitivity of a foil which does not contain ammonium tungstenate and which, immediately after the exposure, is subjected to the action of a mercurous salt solution is arbitrarily taken to be-equal to 100, it will have fallen to 60 after A hour between exposure and aftertreatment and to 20 after 1 hour. However, when ammonium tungstenate was provided, the sensitivity with immediate after-treatment was 200, after hour 200 and after 1 hour 150, and the maximum blackening was considerably higher.

Example IX A foil as used in Example I was sensitized with a solution containing 0.2 mol. dimethoxy-3,4 benzene diazosulphonic acid sodium-l and 0.1 mol. benzene sulphonic acid lead per liter of water and then dried.

The subsequent exposure, after-treatment and development were efiected as in Example I. If the sensitivity of the foil without the antiregression agent is arbitrarily taken to be 100 in the case of an after-treatment following immediately after-exposure, it was after 4 hour between exposure and after-treatment 35.

In the presence of the benzene sulphonic acid lead these sensitivities were 140, 17 and 170 respectively.

Example X A foil as used in Example I was sensitized with a solution containing 0.2 mol. p-rnethoxy benzene sulphonic acid sodium and 0.1 mol. cadmium lactate per liter of water and then dried.

Exposure, after-treatment and development Were effected as described in Example I.

The sensitivity of the foil, treated with the mercurous nitrate solution immediately after exposure was, expressed in terms of the scale of Example I, 230; after /4 hour and 1 hour between exposure and after-treatment 170 and respectively.

While the invention has been described in connection with specific examples and in specific applications, other modifications thereof will be readily apparent to those skilled in the art without departing from the invention as defined in the appended claims.

What we claim is:

l. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive system containing a light-sensitive diazosulphonate and an antiregression agent other than said diazosulphonate consisting of a Water-soluble salt of a metal selected from the group consisting of lead, lanthanum, thorium, uranium, cadmium, zinc, copper, cobalt and chromium, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physicallyintensifiablecontrast?" I 2. A method of producing photographic contrasts form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physically intensifiable contrast.

3. A method of producing photographic contrasts which comprises the steps of selectively exposing 'portions of a light-sensitive system containing a light-sensitive diazosulphonate and an antiregression agent other than said diazosulphonate consisting of a water-soluble salt of cadmium, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physically intensifiable contrast.

4. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive system containing a light-sensitive diazosulphonate and an antiregression agent other than said diazosulphonate consisting of a water soluble salt of zinc, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble which comprises the steps of selectively exposing portionsof a light-sensitive system containing a' light-sensitive diazosulphonate and an antiregressionagent consisting of zinc acetate, to decompose said diazosulphonate and form a stable light decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physically intensifiable contrast. I

8. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive system containing a light-sensitive mercurous salt in the presence of moisture to form a physically intensifiable contrast.

5. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive system containing a light-sensitive diazosulphonate and an antiregression agent other than said diazosulphonate consisting of a water soluble salt of lead, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physically intensifiable contrast.

6. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive system containing a light-sensitive diazosulphonate and an antiregression agent other than said diazosulphonate consisting of a water soluble salt of copper, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physically intensifiable contrast.

7. A method of producing photographic contrasts form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physically intensifiable contrast.

9. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive system containing a light-sensitive diazosulphonate and an antiregression agent consisting of chromic acetate, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physically intensifiable contrast.

10. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive system containing a light-sensitive diazosulphonate and an antiregression agent other than said diazosulphonate consisting of a lead salt of an aromatic sulfonic acid to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physically intensifiable contrast.

11. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive system containing a light-sensitive diazosulphonate and an antiregression agent consisting of a lead salt of napthalene bisulfonic acid, to decompose said diazosulphonate and form a stable lightdecomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form a physically intensifiable contrast.

References Cited in the file of this patent UNITED STATES PATENTS 2,067,690 Alink et al Jan. 12, 1937 2,183,447 Dippel et al Dec. 12, 1939 2,616,803 Ravich Nov. 4, 1952 

1. A METHOD OF PRODUCING PHOTOGRAPHIC CONTRAST WHICH COMPRISES THE STEPS OF SELECTIVELY EXPOSING PORTIONS OF A LIGHT-SENSITIVE SYSTEM CONTAINING A LIGHT-SENSITIVE DIAZOSULPHONATE AND AN ANTIREGRESSION AGENT OTHER THAN SAID DIAZOSULPHONATE CONSISTING OF A WATER-SOLUBLE SALT OF A METAL SELECTED FROM THE GROUP CONSISTING OF LEAD, LANTHANUM, THORIUM, URANIUM, CADMIUM, ZINC, COPPER, COBALT AND CHRMIUM, TO DECOMPOSE SAID DIAZOSULPHONATE AND FORM A STABLE LIGHT-DECOMPOSITION PRODUCT AND SUBJECTING SAID LIGHT-DECOMPOSITION PRODUCT TO THE ACTION OF A SOLUBLE MERCUROUS SALT IN THE PRESENCE OF MOISTURE TO FORM A PHYSICALLY INTENSIFIABLE CONTRAST. 